This specification relates to three dimensional (3D) structures and 3D modeling programs, such as computer-aided design (CAD) applications used with 3D printing.
CAD software has been developed and used to generate two dimensional (2D) and 3D representations of objects. Such 3D representations of objects have employed various modeling techniques to represent the 3D object. In general, 3D models can be divided into two categories: (1) solid models that represent volumes of the object, and (2) shell models that represent the boundaries between solid and non-solid parts of the 3D object. In addition, such 3D models have been used in traditional subtractive manufacturing as well as more recent additive manufacturing, such as 3D printing using different types of materials.
Further, a particular type of material is an auxetic material, which is a material that has a negative Poisson ratio. FIG. 1 shows a comparison of a conventional material 110 with an auxetic material 120. Unlike conventional materials, when an auxetic material is stretched (or compressed) in one direction, instead of becoming thinner (or thicker), it becomes thicker (or thinner) in perpendicular directions. Thus, as shown in FIG. 1, when a compressive load 112 is placed on the conventional material 110, the material 110 expands 114. In contrast, when a compressive load 122 is placed on the auxetic material 120, the material 120 shrinks 124.
Typical auxetic structures are designed with a single polymer. Their fabrication process typically allows only one repetitive cellular unit configuration. In addition, beyond the negative Poisson ratio, auxetic material has been demonstrated to have enhanced mechanical properties, such as shear resistance, indentation resistance, and fracture toughness. It has also demonstrated an enhanced sound and vibration absorption property.